Known radially expandable intravascular stents include a cylindrically shaped sleeve having a first diameter which is placed over a collapsed balloon catheter and then inserted into an occluded or partially occluded blood vessel of interest. Upon inflation of the balloon to a specific pressure, the stent is permanently deformed to a larger second diameter and into contact and support with the interior walls of the blood vessel. After subsequent deflation of the balloon and removal of the catheter, the implanted stent remains supported to the interior wall of the blood vessel at the expanded second diameter.
Intravascular stents such as described in U.S. Pat. No. 4,733,665, issued to Palmaz, included a number of interconnected elongate elements, made from a material such as stainless steel or tantalum, which are arranged and welded in a criss-cross arrangement to form a unitary cylindrical structure. An implanted stent of this construction is shown in FIG. 1 as positioned in an occluded blood vessel of interest. After inflation of the collapsed catheter balloon, however, the overall radial expansion of the instant stent creates a corresponding lateral or axial shrinkage, as shown in FIG. 2, whereby the net result may be a less than successful implantation procedure.
Stents, such as those described by Palmaz, are designed to be expanded only a single time and only to a specific diameter. Therefore, even properly implanted stents of this type may not produce a satisfactory result, particularly in procedures involving children, having blood vessels which will naturally increase in size over time. That is, additional axial shrinkage will occur upon reexpanding of the implanted stent to compensate for the growing blood vessel.
It would be preferred to be able to implant an intravascular stent capable of further radial expansion to at least one greater radial diameter, at a later time as needed. More preferably, it would be preferable to provide a stent capable of radial expansion with a minimum of axial shrinkage.